Fiber-reinforced polyvinyl chloride (PVC) compositions are difficult to make due to the incompatibility of the fibrous materials such as glass fibers in the PVC matrix and the processing difficulties, such as increased melt viscosity, that leads to thermal degradation of the PVC during processing. The compositions of the present disclosure overcome these processing difficulties and allow for a wider range of processing methods to be used including calendering, injection molding, and profile and sheet extrusion. Also, historically, commercially available glass fiber filled PVC formulations have been limited to a glass fiber content of 30% or less. The improved compositions and processing methods in the present disclosure allow for fiber content up to 65% thus improving the physical properties, such as tensile and flexural modulus, of the PVC compositions.